1. Field of the Invention
The present invention relates to a starter with an overheat-protection device including a brush device having a thermostat adapted to interrupt energization of a starting motor when a brush in the starting motor continuously energized exceeds a predetermined temperature due to self-heating of the brush, whereby the energization of the stating motor with a power supply is interrupted.
2. Description of the Related Art
FIG. 14 is a cross-sectional view of the essential part of a conventional starter. FIG. 15 is a perspective view of a heat-reception member shown in FIG. 14. FIG. 16 is an electric circuit diagram of the starter of FIG. 14.
In FIG. 14, a starting motor 1 comprises a shaft 2 rotatably supported by a bearing 5, an armature 3 fixed to the shaft 2, plural commutator pieces 4 arranged adjacently to the armature 3 and in the periphery of the shaft 2, brushes 6 having a substantially parallelepiped rectangular shape, in contact with the commutator pieces 4 at four positions thereof, and brush holders 7 slidably supporting the brushes 6.
The starting motor 1 is supported in a bracket 8. Bases 9 are fixed to the bracket 8. Each brush holder 7 is fixed to the base 9 via an insulation plate 10, which is an electric insulation member, and a heat-reception member 11 by means of rivets.
The heat-reception member 11, formed by working a brass flat sheet, contains a plane portion 11a having holes 11c for fixing the rivets, sandwiched between the brush holder 7 and the insulation sheet 10, and a thermostat-attachment portion 11b bent perpendicularly, immediately from the plane portion 11a, and extending therefrom.
A thermostat 12 is fixed to the thermostat-attachment portion 11b via an insulation tube 13 by means of an adhesion tape 14. The insulation tube 13 covers the thermostat 12 so that the thermostat 12 is prevented from directly contacting the heat-reception member 11. Thus, the electric insulation of the thermostat 12 from the brush 6 and the bracket 8 is secured.
The thermostat 12 comprises a case 15 and a bimetal 18 housed in the case 15. The bimetal 18, when the temperature exceeds a predetermined value, is bent-distorted to interrupt the energization.
In FIG. 16, the starter is provided with the starting motor 1, a battery 30 as a power supply, a start-switch 31 provided as a key switch, an auxiliary switch 32, the thermostat 12 connected in series with the auxiliary switch 32, and a magnet switch 36.
The auxiliary switch 32 comprises a pair of fixed contacts 33, a movable contact 34, and an excitation coil 35.
The magnet switch 36 comprises a pair of main fixed contacts 37, a main movable contact 38 interlocked with a plunger (not shown) to contact the main fixed contacts 37 and turn on-off a main current to the starting motor 1, an attraction coil 39 which becomes a resistor for a fine current flowing into the starting motor 1 till a pinion gear becomes engaged (for the time till the main movable contact 38 contacts the main fixed contact 37) and also having a function of generating an attraction force which causes the pinion gear (not shown) to be engaged with the ring gear of an internal combustion engine, and a holding coil 40 for holding the contact of the main movable contact 38 with a pair of the main fixed contacts 37.
From the thermostat 12, a lead wire 17 connected to an excitation coil 35, and also, a lead wire 16 connected to a connector 21 are led out, respectively.
Hereinafter, operation of the starter configured as described above will be described. First, when a driver turns on the start switch 31 by operation of the key switch, current flows from the battery 30 into the thermostat 12 and the excitation coil 35, so that the excitation coil 35 is excited. As a result, the movable contact 34 is moved, so that the fixed contacts 33 are electrically connected to each other, and the auxiliary switch 32 becomes on. At the same time, fine current flows from the battery 30 into the starting motor 1 via the attraction coil 39, so that the starting motor 1 is driven at a low rotation speed, and current also flows into the holding coil 40.
When the current flows into the attraction coil 39, an attraction force is generated in the attraction coil 39. With the attraction force, the plunger is moved, and a shift lever engaged and stopped at the end of the plunger is rotated to press the pinion gear toward the ring gear side of the internal combustion engine, so that the pinion gear is engaged with the ring gear. Also, the main movable contact 38 is interlocked with the plunger. The main movable contact 38 is interlocked with the plunger. When the pinion gear becomes normally engaged with the ring gear, the main movable contact 38 comes into contact with the main fixed contact 37, and main current from the battery 30 flows directly into the starting motor 1, so that the starting motor 1 is rotated, and the internal combustion engine starts.
After the internal combustion engine starts, the start switch 31 is turned off by driver""s operation of the key switch, so that the energization of the auxiliary switch 32, the magnet switch 36, and the starting motor 1 by means of the battery 30 is interrupted. As a result, the attraction force at the attraction coil 39 becomes null, the engagement of the pinion gear with the ring gear is released, and rotation of the starting motor 1 stops.
In the event that the start switch 31 is not turned off, caused by a defect in return of the key switch or the like, so that current continues to flow from the battery 30 into the starting motor after the internal combustion engine starts, for example, there is the danger that thermal damages such as dielectric breakdown between the armature 1 and the commutator pieces 4 of the starting motor 1, or the like may occur.
To prevent such excessively continuous energization of the starting motor 1, the thermostat 12 is contained in the starter.
If current continues to flow in the starting motor 1 after the internal combustion engine starts, heat (hereinafter, referred to as brush heat) is generated in each of the brushes 6 so that the brush 6 have a high temperature. The heat is conducted to the thermostat 12 via the heat reception member 11 so that the temperature of the thermostat 12 rises. When the thermostat 12 reaches a predetermined temperature or higher, the bimetal 18 is bent-distorted to interrupt the energization, and the excitation of the excitation coil 35 becomes null. The movable contact 34 is separated from the fixed contact 33, and the auxiliary switch 32 becomes off. As a result energization of the attraction coil 39, the starting motor 1, and the holding coil 40 becomes null. Thus, thermal damages such as dielectric breakdown between the armature 3 and the commutation pieces 4 of the starting motor 1 can be prevented.
The insulation plate 10 is provided between the heat reception member 11 and the base 9. Thus, heat is suppressed from escaping from the base 9 side. Thus, the brush heat is ready to be conducted to the thermostat 12.
In the starter having the above-described configuration, the brush heat is conducted to the thermostat 12 via the heat reception member 11. However, since the heat reception member 11 has a heat resistance, and there is a distance between the brush 6 and the thermostat 12, the thermostat 12 can not quickly respond to a rise in temperature of the brush heat by any means. Accordingly, there arises the problem that current continues to flow in the starting motor 1 though the brush 6 exceeds a predetermined temperature, and thermal damages such as dielectric breakdown between the armature 1 and the commutator pieces of the starting motor 1 become severer.
As a countermeasure against the above problem, the response time of the thermostat operating based on the brush heat can be reduced by selecting such a bimetal as can operate at a lower temperature. For example, the response temperature of 120xc2x0 C. to 150xc2x0 C. can be reduced to 100xc2x0 C. However, the starter is required to start an internal combustion engine in the high temperature environment at about 100xc2x0 C., depending on the use conditions of the internal combustion engine. Accordingly, this countermeasure is unprofitable.
To solve the above-described problems, the present invention has been devised. It is an object of the present invention to provide a starter with an overheat-protection device including a brush device for securely preventing overheat of a starting motor.
To this end, according to the present invention, there is provided a starter with an overheat protection device including a brush device provided with brush holders, brushes slidably supported in the brush holders, respectively, springs contacting one faces of the brushes to press the brushes in the radial, inner directions, thermostats attached directly or indirectly to the brushes and adapted to interrupt energization of a starting motor caused by a power supply when the brushes exceed a predetermined temperature, caused by the starting motor continuously energized with the power supply.